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The effect of composition and cation ordering on the compressibility of columbites up to 7 GPa |
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| Authors: | M Pistorino F Nestola T Boffa Ballaran M C Domeneghetti |
| Institution: | 1. Dipartimento di Scienze della Terra, Universitá degli Studi di Pavia, via Ferrata 1, 27100, Pavia, Italy 2. Bayerisches Geoinstitut, Universit?t Bayreuth, 95440, Bayreuth, Germany 3. Dipartimento di Mineralogia e Petrologia, Università di Padova (Italy), Corso Garibaldi 37, 35137, Padova, Italy |
| Abstract: | The unit-cell parameters of two columbite samples along the (Fe,Mn)Nb2O6 solid solution were measured by means of high-pressure single-crystal X-ray diffraction up to pressures of 7 GPa. The compressional behaviour of these minerals was studied as a function of composition and degree of order. The P–V data of all the samples were fitted with a third-order Birch–Murnaghan equation of state. For the two samples with different compositions but identical degree of order the substitution of Mn for Fe causes a decrease of the bulk modulus K T0, from 153(1) to 146(1) GPa, without any effect on the pressure first derivative K′. For the two samples with the same composition, cation ordering causes an increase of the bulk modulus from 149(1) to 153(1) GPa and of the pressure first derivative from 4.1(2) to 4.8(3). The compressional behaviour is anisotropic with a linear axial compressibility scheme β b > β c ≥ β a for all samples, regardless of composition and degree of order. Such anisotropy increases sligthly with increasing Mn content. |
| Keywords: | Columbites High-pressure behaviour Single-crystal X-ray diffraction |
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